Nacreous pigments produce pearl-like, metallic, and iridescent effects. Natural pearl essence, a mixture of guanine and hypoxanthine obtained from the scales of fish, has long been used in cosmetic formulations. Synthetic nacreous pigments developed for cosmetic use include mica-based pigments and bismuth oxychloride, or bismuth oxychloride-mica. Muscovite mica platelets coated with a metallic oxide, such as titanium dioxide have been widely used. A relatively thin titanium dioxide coating produces a pearl-like or silvery luster. Mica platelets with thicker coatings produce color, even though the components are colorless, through the phenomenon of light interference; they are known as interference pigments. The color, called the reflection color, is seen most effectively by specular or mirror-like reflection, where the angle of reflection equals the angle of incidence. The reflection color is a function of optical thickness, i.e. the geometrical thickness times the refractive index, of the coating. Optical thickness of about 100 nm to about 160 nm produce reflections which may be called white, silvery or pearly; optical thickness of about 190 nm or more produce colored reflections.
Nacreous or pearlescent pigments containing mica or mica coated with titanium dioxide are known in the art. Reference is made, e.g., to U.S. Pat. Nos. 3,087,828 3,926,659; 4,146,403; 4,192,691; 4,744,832; 5,273,576; 5,433,779; 5,456,749; and 6,899,757. Each of these patents is incorporated by reference herein in its entirety.
The bismuth oxychloride-mica powders have the advantage of softness, good compressibility and high luster. Bismuth oxychloride-mica pigments are made by precipitating bismuth oxychloride crystals in the presence of mica. In general terms, this is accomplished by hydrolyzing a soluble bismuth compound in an aqueous slurry of mica. While there are a number of ways of accomplishing this, a preferred procedure is to first prepare an acidic slurry of wet ground mica to which is added a solution of a soluble bismuth salt. The bismuth compound hydrolyses to form a bismuth oxychloride precipitate. The acidity of the system is maintained by adding a solution of a base, such as sodium hydroxide, for neutralization of the acid formed by the hydrolysis reaction. The amount of the bismuth solution is controlled so as to obtain the desired ratio of BiOCl to mica, generally in the range of 1:4 to 4:1, preferably 1:1.5 to 1.5:1. Reference is made to U.S. Pat. No. 3,980,491 regarding preparation of BiOCl pigments. The appearance and feel of bismuth oxychloride pigments make these pigments popular with consumers. However, these pigments have been perceived by some consumers to cause skin irritation. Consequently, it has become desirable to develop non-BiOCl pigments which have the luster and feel of BiOCl pigments.
Combination pigments are mare complex than the mica-based and BiOCl interference pigments. In combination pigments, the oxide-coated mica pigment is further coated with an absorption pigment or dye, so-called because it absorbs some portion of the visible spectrum. If the absorption colorant has the same hue as the reflection color of the oxide-mica pigment, that color is intensified and is seen over a wide range of angles; if it has a different hue, the reflection color or a color close to it is seen at the specular angle, whereas the hue of the absorption pigment is seen at other angles. In some cases, transition colors may be seen between the extremes. Thus a single pigment has more than one color. The absorption colorant coat should be uniform and should adhere firmly to the oxide-coated mica particles.
In known combination pigments, the desired results are achieved by depositing the colorant or a precursor on the pigment platelets from aqueous solution. For example, U.S. Pat. No. 4,309,480 teaches that iron blue (ferric ferrocyanide) may be precipitated onto TiO2-coated mica by the reaction of ferric chloride and potassium ferrocyanide in aqueous solution. Aluminum hydroxide may be precipitated after the iron blue or simultaneously with it, but it is not required for the formation of the iron blue coating. U.S. Pat. No. 3,951,679 shows that an Fe(II) phosphate layer may be precipitated onto mica pigments from aqueous solution and then converted in place to ferrous ferrocyanide by reaction with ferrocyanide solution, followed by oxidation in place to ferric ferrocyanide. U.S. Pat. No. 4,084,983 describes the formation of colored lakes on mica pigments by first depositing aluminum hydroxide on the surface from soluble reactants and then reacting with a dye in solution. Other combination pigments and methods of manufacturing same are disclosed in U.S. Pat. Nos. 5,885,342 and 6,129,784.
In U.S. Pat. No. 4,755,229, a combination pigment is prepared by providing an aqueous dispersion of the colored pigment containing an anionic polymeric substance, such as albumin or xanthan gum, and adding the dispersion to a suspension of the mica or oxide-coated mica pigment. The hydrous oxide of a polyvalent metal, for example chromium(III) or aluminum(III), is then produced by the simultaneous addition of a solution of the metal salt and of a basic solution. The dispersed pigment particles and the polymer deposit with the hydrous oxide of the polyvalent metal to form a smooth, adherent, uniform coating on the mica platelets. It is believed that the polymer reacts with the polyvalent metal to form a complex hydrous oxide.
The appearance and feel of mica or titanium-dioxide-coated-mica pigments are perceived by consumers to be inferior to those of BiOCl pigments. Accordingly, it is desirable to provide mica and titanium-dioxide-coated mica pigments having the appearance and feel of bismuth oxychloride. Until the present invention, mica-based pigments have not been provided with the look, e.g. optical properties, and feel of BiOCl pigments.